A method and a grinding machine of the type specified above are well-known in the art.
During the centerless grinding, it is conventional to position a rotatable workpiece on a support between a grinding wheel and a regulating wheel. The grinding wheel is brought into engagement on a peripheral surface of the workpiece while the latter is simultaneously supported by the regulating wheel.
In this context, it is further known to machine workpieces by angular plunge grinding. During angular plunge grinding, the grinding wheel axis is inclined relative to the longitudinal axis of the workpiece by a predetermined angle. The outer periphery of the grinding wheel is conical in this situation, such that the surface line of the conical section of the grinding wheel e.g. extends parallel to the axis of the workpiece which, in turn, makes it possible to grind cylindrical peripheries.
In this context it is, further, known to grind workpieces having axial sections of different diameters. Between these diameters are shoulders being either configurated as annular shoulders having surfaces extending in a radial plane or having inclined shoulders with conical surfaces but, in both cases, interconnecting cylindrical sections of different diameter.
For the angular plunge grinding of such workpieces, it is known to axially support the workpieces on the support rail, i.e. to push the workpieces against an axial stop during angular plunge grinding.
In conventional centerless angular plunge grinding, the grinding wheel is fed-in in a direction being inclined to the workpiece axis for removing a predetermined overmeasure on the periphery of the workpiece. In this context, it is known to align the workpiece together with the support in an orientation being inclined to the longitudinal median plane of the grinding machine, namely on a slide that may be displaced in a direction extending under right angles to the workpiece axis. The regulating wheel, in turn, is disposed on a second slide being arranged on the afore-mentioned first slide and being adapted to be displaced parallel to the feed-in direction of the latter, enabling to push the regulating wheel against the workpiece in a radial direction relative to the workpiece axis. In this prior art grinding machines, the grinding spindle is rigidly attached to the machine bed. The rotational axis of the grinding wheel extends parallel to the longitudinal median plane of the grinding machine. The grinding wheel is configurated conically at its periphery, the cone angle being exactly the same as the angular inclination of the workpiece relative to the longitudinal median plane of the grinding machine.
In this prior art approach, there is the risk that the grinding wheel will come into engagement only with the overmeasure in the area of the shoulder at the beginning of the process and will, hence, remove this overmeasure, whereas it does not come into contact with the cylindrical section of the workpiece overmeasure. As a consequence, a non-defined relative position may develop between the workpiece, the regulating wheel, the grinding wheel and the support rail which under the action of the grinding pressure acting against the shoulder, may result in a sudden movement of the workpiece and, hence, in undesired movements. Moreover, the drive effecting the rotation of the workpiece via the regulating wheel may not be guaranteed in this situation due to the very low radial force exerted solely via the grinding wheel contact to the workpiece shoulder.
Moreover, the prior art approach has the disadvantage that the amount of overmeasure in the area of the cylindrical sections and in the area of the shoulder are depending on one another, namely over the inclined angle under which the grinding wheel and the workpiece are fed-in relative to one another.
EP 0 548 957 A1 discloses a method and a grinding machine for centerless grinding workpieces having a stepped diameter. The cylindrical sections of different diameter are ground by separate grinding wheels, wherein the separate grinding wheels are driven separately. By appropriately setting the rotational speed, the peripheral speeds and, hence, the cutting speeds of the grinding wheels may be made equal in spite of the different diameters of the grinding wheels. According to this prior art method, an approach is disclosed relating to the grinding of shoulder sections in such stepped workpieces. In an example, a workpiece is ground having a cylindrical section of a smaller diameter, a cylindrical section of larger diameter as well as a rounded shoulder configurating a transition therebetween. For centerless grinding this workpiece, a grinding wheel of complementary shape is utilized. In a first machining step, the grinding wheel is approached to the workpiece in a radial direction by feeding-in the regulating wheel accordingly. As a result, the grinding wheel comes into engagement with the workpiece section of larger diameter first, namely with the grinding wheel of smaller diameter. The feeding-in continues until the grinding wheel contacts the workpiece over its entire length. The grinding wheel is then displaced in an axial direction until the final dimensions of the workpiece are attained. Therefore, this prior art method is not an angular plunge grinding process and an axial feed-in movement of the grinding wheel is only effected during the last method step whereas the radial feed-in movement is not effected by the grinding wheel, but by the regulating wheel instead.
DE 40 02 632 C2 generally teaches that during centerless cylindrical grinding, the grinding wheel may either be fed-in solely radially or solely axially or simultaneously radially and axially, and that feeding-in movements may also be effected through the regulating wheel.
It is, therefore, an object underlying the invention to improve a method and a grinding machine of the type specified at the outset such that the disadvantages mentioned before are avoided.
In particular, a safe position support and contact of the workpiece shall be guaranteed at any time so that only one well-defined movement of the workpiece is possible. Moreover, it shall be ensured that the workpiece is applied against the regulating wheel to a sufficient extent by a corresponding radial force, thus guaranteeing the rotational drive of the workpiece. Finally, it shall be possible to separately set the amount of overmeasure in the area of the cylindrical sections of the workpiece and of the shoulder, depending on the particular application.